Polymer for heat-sensitive lithographic printing plate precursor

ABSTRACT

A polymer for a heat-sensitive lithographic printing plate precursor is disclosed wherein the polymer comprises a phenolic monomeric unit wherein the phenyl group of the phenolic monomeric unit is substituted by a group having the structure —S-(L) k -Q wherein S is covalently bound to a carbon atom of the phenyl group, L is a linking group, k is 0 or 1 and Q comprises a heterocyclic group and wherein the substitution of the polymer increases the chemical resistance of the coating of the printing plate precursor.

FIELD OF THE INVENTION

The present invention relates to a polymer for a heat-sensitivelithographic printing plate precursor.

BACKGROUND OF THE INVENTION

Lithographic printing presses use a so-called printing master such as aprinting plate which is mounted on a cylinder of the printing press. Themaster carries a lithographic image on its surface and a print isobtained by applying ink to said image and then transferring the inkfrom the master onto a receiver material, which is typically paper. Inconventional, so-called “wet” lithographic printing, ink as well as anaqueous fountain solution (also called dampening liquid) are supplied tothe lithographic image which consists of oleophilic (or hydrophobic,i.e. ink-accepting, water-repelling) areas as well as hydrophilic (oroleophobic, i.e. water-accepting, ink-repelling) areas. In so-calleddriographic printing, the lithographic image consists of ink-acceptingand ink-abhesive (ink-repelling) areas and during driographic printing,only ink is supplied to the master.

Printing masters are generally obtained by the so-calledcomputer-to-film method wherein various pre-press steps such as typefaceselection, scanning, color separation, screening, trapping, layout andimposition are accomplished digitally and each color selection istransferred to graphic arts film using an image-setter. Afterprocessing, the film can be used as a mask for the exposure of animaging material called plate precursor and after plate processing, aprinting plate is obtained which can be used as a master.

A typical printing plate precursor for computer-to-film methods comprisea hydrophilic support and an image-recording layer of a photosensitivepolymer layers which include UV-sensitive diazo compounds,dichromate-sensitized hydrophilic colloids and a large variety ofsynthetic photopolymers. Particularly diazo-sensitized systems arewidely used. Upon image-wise exposure, typically by means of a film maskin a UV contact frame, the exposed image areas become insoluble and theunexposed areas remain soluble in an aqueous alkaline developer. Theplate is then processed with the developer to remove the diazonium saltor diazo resin in the unexposed areas. So the exposed areas define theimage areas (printing areas) of the printing master, and such printingplate precursors are therefore called ‘negative-working’. Alsopositive-working materials, wherein the exposed areas define thenon-printing areas, are known, e.g. plates having anovolac/naphtoquinone-diazide coating which dissolves in the developeronly at exposed areas.

In addition to the above photosensitive materials, also heat-sensitiveprinting plate precursors have become very popular. Such thermalmaterials offer the advantage of daylight-stability and are especiallyused in the so-called computer-to-plate method wherein the plateprecursor is directly exposed, i.e. without the use of a film mask. Thematerial is exposed to heat or to infrared light and the generated heattriggers a (physico-)chemical process, such as ablation, polymerization,insolubilisation by cross-linking of a polymer, heat-inducedsolubilisation, decomposition, or particle coagulation of athermoplastic polymer latex.

The known heat-sensitive printing plate precursors typically comprise ahydrophilic support and a coating containing an oleophilic polymer,which is alkali-soluble in exposed areas (positive working material) orin non-exposed areas (negative working material) and an IR-absorbingcompound. Such an oleophilic polymer is typically a phenolic resin.

WO99/01795 describes a method for preparing a positive working resistpattern on a substrate wherein the coating composition comprises apolymeric substance having functional groups such that thefunctionalised polymeric substance has the property that it is developerinsoluble prior to delivery of radiation and developer solublethereafter. Suitable functional groups are known to favor hydrogenbonding and may comprise amino, amido, chloro, fluoro, carbonyl,sulphinyl and sulphonyl groups and these groups are bonded to thepolymeric substance by an esterification reaction with the phenolichydroxy group to form a resin ester.

EP-A 0 934 822 describes a photosensitive composition for a lithographicprinting plate wherein the composition contains an alkali-soluble resinhaving phenolic hydroxyl groups and of which at least some of thephenolic hydroxyl groups are esterified by a sulphonic acid or acarboxylic acid compound.

EP-A 1 072 432 describes an image forming material which comprises arecording layer which is formed of a composition whose solubility inwater or in an alkali aqueous solution is altered by the effects oflight or heat. This recording layer comprises a polymer of vinyl phenolor a phenolic polymer, wherein hydroxy groups and alkoxy groups aredirectly linked to the aromatic hydrocarbon ring. The alkoxy group iscomposed of 20 or less carbon atoms.

U.S. Pat. No. 5,641,608 describes a direct process for producing animaged pattern on a substrate surface for printed circuit boardapplication. The process utilises a thermo-resist composition whichundergo a thermally-induced chemical transformation effective either toablate the composition or to increase or decrease its solubility in aparticular developer. The thermo-resist composition comprises phenolicpolymers in which free hydroxyl groups are protected. Upon heating inthe presence of an acid these protecting groups split off resulting in asolubility change of the composition. In positive thermo-resists thehydroxyl protecting groups may be ethers, such as alkyl-, benzyl-,cycloalkyl- or trialkylsilyl-ethers, and oxy-carbonyl groups.

EP-A 0 982 123 describes a photosensitive resin composition or recordingmaterial wherein the binder is a phenolic polymer which is substitutedwith a specific functional group on the aromatic hydrocarbon ring suchas a halogen atom, an alkyl group having 12 or less carbon atoms, analkoxy group, an alkylthio group, a cyano group, a nitro group and atrifluoromethyl group or wherein the hydrogen atom of the hydroxy groupis substituted with a specific functional group such as an amide, athioamide and a sulphonamide group. As a result, the film thus formedhas such a high density that improves the intra-film transistivity ofheat obtained by the light-to-heat conversion at the time of laserexposure. The high density of the film makes the image recordingmaterial less susceptible to external influences such as humidity andtemperature. Consequently, the storage stability of the image recordingmaterial can also be enhanced.

The ink and fountain solution which are supplied to the plate during theprinting process, may attack the coating and, consequently, theresistance of the coating against these liquids, hereinafter referred toas “chemical resistance”, may affect the printing run length. The mostwidely used polymers in these coatings are phenolic resins and it hasbeen found in the above prior art that the printing run length can beimproved by modifying such resins by a chemical substitution reaction onthe hydroxyl group of the phenolic group. However, this modificationreaction decreases the number of free hydroxyl groups on the polymer andthereby reduces the solubility of the coating in an alkaline developer.The modification reaction proposed in the present invention enables toincrease the chemical resistance of the coating without substantiallyreducing the developability of the coating.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a polymer comprisinga phenolic monomeric unit wherein the phenyl group of the phenolicmonomeric unit is substituted by a group having the structure—S-(L)_(k)-Q wherein S is covalently bound to a carbon atom of thephenyl group, wherein L is a linking group, wherein k is 0 or 1 andwherein Q comprises a heterocyclic group.

It is also an aspect of the present invention to provide a polymer asdefined in claim 1, for a heat-sensitive lithographic printing plateprecursor wherein the chemical resistance of the heat-sensitive coatingagainst printing liquids and press chemicals is improved.

Specific embodiments of the invention are defined in the dependentclaims.

DETAILED DESCRIPTION OF THE INVENTION

In order to obtain a heat-sensitive lithographic printing plate with animproved printing run length, it is important to increase the chemicalresistance of the heat-sensitive coating against the printing liquidssuch as the dampening liquid and ink, and against the press chemicalssuch as cleaning liquids for the plate, for the blanket and for thepress rollers. These printing properties are affected by the compositionof the coating wherein the type of polymer is one of the most importantcomponents for this property.

In accordance with the present invention, there is provided a polymer,which comprises a phenolic monomeric unit wherein the phenyl group ofthe phenolic monomeric unit is substituted by a group having thestructure —S-(L)_(k)-Q wherein S is covalently bound to a carbon atom ofthe phenyl group, wherein L is a linking group, wherein k is 0 or 1 andwherein Q comprises a heterocyclic group.

It is also an aspect of the present invention that there is provided aheat-sensitive lithographic printing plate precursor comprising asupport having a hydrophilic surface and an oleophilic coating, saidcoating comprising this polymer and an infrared absorbing agent.

It is also an aspect of the present invention that the oleophiliccoating comprising this polymer has an increased chemical resistance dueto the modification of the polymer by this specified substituting grouphaving the structure —S-(L)_(k)-Q wherein S is covalently bound to acarbon atom of the phenyl group, wherein L is a linking group, wherein kis 0 or 1 and wherein Q comprises a heterocyclic group. This chemicalresistance can be measured by tests described in the examples.

In accordance with a preferred embodiment of the present invention, theheterocyclic group is aromatic.

In accordance with another preferred embodiment of the presentinvention, the heterocyclic group contains at least one nitrogen atom inthe ring of the heterocyclic group.

In accordance with another preferred embodiment of the presentinvention, the heterocyclic group has a 5- or 6-membered ring structure,optionally annelated with another ring system.

In accordance with another preferred embodiment of the presentinvention, the heterocyclic group is selected from an optionallysubstituted tetrazole, triazole, thiadiazole, oxadiazole, imidazole,benzimidazole, thiazole, benzthiazole, oxazole, benzoxazole, pyrazole,pyrrole, pyrimidine, pyrasine, pyridasine, triazine or pyridine group.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein Z represents the necessary atoms to form a 5- or 6-memberedheterocyclic aromatic group, optionally annelated with another ringsystem.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein R¹ is selected from hydrogen or an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula.

wherein n is 0, 1, 2, 3, 4 or 5,wherein each R is independently selected from hydrogen, an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R²,—NH—SO₂—R⁵, —CO—NR²—R³, —NR²—CO—R⁵, —NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴,—NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁵, —CO—O—R², —CO—R², —SO₃—R²,—O—SO₂—R⁵, —SO₂—R², SO—R⁵, —P(═O) (—O—R²) (—O—R³) —O—P(═O) (—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R², —CN, —NO₂ or -M—R², wherein M representsa divalent linking group containing 1 to 8 carbon atoms,wherein R² to R⁴ are independently selected from hydrogen or anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group,wherein R⁵ is an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup,or wherein at least two groups selected from each R¹, R², R³, R⁴ and R⁵together represent the necessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein X is O, S or NR³,wherein R¹ is selected from hydrogen, an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen or -L¹—R²,wherein L¹ is a linking group,wherein R² is selected from hydrogen, an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen or —CN,wherein R³ is selected from hydrogen or an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group,or wherein at least two groups selected from R¹, R² and R³ represent thenecessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein X is O, S or NR^(4,)wherein R² and R² are independently selected from hydrogen, anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogenor -L¹—R³,wherein L¹ is a linking group,wherein R³ is selected from hydrogen, an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen or —CN,wherein R⁴ is selected from hydrogen or an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group,or wherein at least two groups selected from R¹, R², R³ and R⁴ togetherrepresent the necessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein n is 0, 1, 2, 3 or 4, wherein X is O, S or NR⁵,wherein each R¹ is independently selected from hydrogen, an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R²,—NH—SO₂—R⁶, —CO—NR²—R³, —NR²—CO—R⁶, —NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴,—NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁶, —CO—O—R², —CO—R², —SO₃—R²,—O—SO₂—R⁶, —SO₂—R², —SO—R⁶, —P(═O) (—O—R²) (—O—R³), —O—P(═O) (—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R², —CN, —NO² or -M—R², wherein M representsa divalent linking group containing 1 to 8 carbon atoms,wherein R² to R⁵ are independently selected from hydrogen or anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group,wherein R⁶ is an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup,or wherein at least two groups selected from each R¹, R², R³, R⁴, R⁵ andR⁶ represent the necessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises the following formula

wherein n is 0, 1, 2 or 3,wherein each R¹ is independently selected from hydrogen, an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R²,—NH—SO₂—R⁵, —CO—NR²—R³, —NR²—CO—R⁵, —NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴,—NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁵, —CO—O—R², —CO—R², —SO₃—R²,—O—SO₂—R⁵, —SO₂—R², —SO—R⁵, —P(═O) (—O—R²) (—O—R³), —O—P(═O) (—O—R²)(—O—R³), —NR²- R³, —O—R², S—R², —CN, —NO₂ or -M—R², wherein M representsa divalent linking group containing 1 to 8 carbon atoms,wherein R² to R⁴ are independently selected from hydrogen or anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group,wherein R⁵ is an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup,or wherein at least two groups selected from each R¹, R², R³, R⁴ and R⁵together represent the necessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group Q further comprises the following substituent

wherein # denotes the bond between said substituent and Q,wherein R^(q) and R^(p) are independently selected from an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, or -L^(r)—R^(t), whereinL^(r) is a linking group,wherein R^(t) is selected from hydrogen, an optionally substitutedalkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,aralkyl or heteroaralkyl group or halogen,or wherein at least two groups selected from R^(q), R^(p) and R^(t)together represent the necessary atoms to form a cyclic structure.

In accordance with another preferred embodiment of the presentinvention, the group Q further comprises the following substituent

wherein # denotes the bond between said substituent and Q,wherein n is 0, 1, 2, 3 or 4,wherein each R^(s) is independently selected from hydrogen, anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogen,—SO₂—NH—R^(x), —NH—SO₂—R^(w), —CO—NR^(x)—R^(y), —NR^(x)—CO—R^(w),—NR^(x)—CO—NR^(y)—R^(z), NR^(x)—CS—NR^(y)—R^(z), —NR^(x)—CO—O—R^(y),—O—CO—NR^(x)—R^(y), —O—CO—R^(w), —CO—O—R^(x), —CO—R^(x), —SO₃—R^(x),—O—SO₂—R^(w), —SO₂—R^(x), —SO—R^(w), —P(═O) (—O—R^(x)) (—O—R^(Y)),—O—P(═O) (—O—R^(x)) (—O—R^(y)) —NR^(x)—R^(y), —O—R^(x), —S—R^(x), —CN,—NO₂ or -M—R^(x), wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms,wherein R^(x), R^(y) and R^(z) are independently selected from hydrogenor an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group,wherein R^(w) is an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup,or wherein at least two groups selected from R^(s), R^(x), R^(y), R^(z)and R^(w) together represent the necessary atoms to form a cyclicstructure.

In accordance with another preferred embodiment of the presentinvention, the group —S-(L)_(k)-Q comprises one of the followingformula:

Examples of linking groups are —CO—, —CO—O—, —CS—, —NR^(a)R^(b)—,—CO—NR^(a)—, —NR^(a)—CO—O—, —NR^(a)—CO—O—, —NR^(a)—CO—NR^(b)—,—NR^(a)—CS—NR^(b)—, —NH—SO₂—, —SO₂—NH—, —(CR^(a)R^(b))t—, an alkylenesuch —CH₂—, —CH₂—CH₂—, —CH₂—(CH₂)_(n)—CH₂—, an arylene such as phenyleneor naphtalene, a divalent heterocyclic group or suitable combinationsthereof. Herein represent n and t an integer between 1 and 8 andrepresent R^(a) and R^(b) a group selected from hydrogen or anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group.

The polymers of this invention can be obtained via several routes, e.g.by reaction of a reactive compound comprising a heterocyclic group witha phenyl group of a polymer containing a phenolic monomeric unit. Thepolymers of this invention can also be obtained by reaction of areactive compound comprising a heterocyclic group with the phenyl groupa phenolic monomer and subsequently polymerising or polycondensatingthis reacted monomer. These pre-modified monomers can preferentially becopolymerised or copolycondensated with other monomers.

Such a reactive compound comprising a heterocyclic group, herein afteralso referred to as a “modifying reagens”, is a compound having theformula X—S-(L)_(k)-Q wherein L is a linking group, wherein k is 0 or 1,wherein Q comprises a heterocyclic group and wherein X represents afunctional group, capable of reacting with the phenyl group of thephenolic unit, or a precursor for such a functional group. Examples ofsuitable functional groups or precursors for this substitution reactionon the phenyl group, are a halogen atom such as Cl, Br or I, or ahydrogen atom which can be replaced by a halogen atom on reaction with ahalogenating compound such as SO₂Cl₂.

Examples of modifying reagens are:

Polymers containing phenolic monomeric units can be a random, analternating, a block or graft copolymer of different monomers and may beselected from e.g. polymers or copolymers of vinylphenol, novolac resinsor resol resins. A novolac resin is preferred.

The novolac resin or resol resin may be prepared by polycondensation ofat least one member selected from aromatic hydrocarbons such as phenol,o-cresol, p-cresol, m-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol,pyrogallol, bisphenol, bisphenol A, trisphenol, o-ethylphenol,p-etylphenol, propylphenol, n-butylphenol, t-butylphenol, 1-naphtol and2-naphtol, with at least one aldehyde or ketone selected from aldehydessuch as formaldehyde, glyoxal, acetoaldehyde, propionaldehyde,benzaldehyde and furfural and ketones such as acetone, methyl ethylketone and methyl isobutyl ketone, in the presence of an acid catalyst.Instead of formaldehyde and acetaldehyde, paraformaldehyde andparaldehyde may, respectively, be used.

The weight average molecular weight, measured by gel permeationchromatography using universal calibration and polystyrene standards, ofthe novolac resin is preferably from 500 to 150,000 g/mol, morepreferably from 1,500 to 15,000 g/mol.

The poly(vinylphenol) resin may also be a polymer of one or morehydroxy-phenyl containing monomers such as hydroxystyrenes orhydroxy-phenyl (meth)acrylates. Examples of such hydroxystyrenes areo-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene,2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and2-(p-hydroxyphenyl)propylene. Such a hydroxystyrene may have asubstituent such as chlorine, bromine, iodine, fluorine or a C₁₋₄ alkylgroup, on its aromatic ring. An example of such hydroxy-phenyl(meth)acrylate is 2-hydroxy-phenyl methacrylate.

The poly(vinylphenol) resin may usually be prepared by polymerizing oneor more hydroxy-phenyl containing monomer in the presence of a radicalinitiator or a cationic polymerization initiator. The poly(vinylphenol)resin may also be prepared by copolymerizing one or more of thesehydroxy-phenyl containing monomers with other monomeric compounds suchas acrylate monomers, methacrylate monomers, acrylamide monomers,methacrylamide monomers, vinyl monomers, aromatic vinyl monomers ordiene monomers.

The weight average molecular weight, measured by gel permeationchromatography using universal calibration and polystyrene standards, ofthe poly(vinylphenol) resin is preferably from 1.000 to 200,000 g/mol,more preferably from 1,500 to 50,000 g/mol.

Examples of polymers containing phenolic monomeric units which can bemodified with a modifying reagens are:

-   POL-01: ALNOVOL SPN452 is a solution of a novolac resin, 40% by    weight in Dowanol PM, obtained from CLARIANT GmbH.-   Dowanol PM consists of 1-methoxy-2-propanol (>99.5%) and    2-methoxy-1-propanol (<0.5%).-   POL-02: ALNOVOL SPN400 is a solution of a novolac resin, 44% by    weight in Dowanol PMA, obtained from CLARIANT GmbH.-   Dowanol PMA consists of 2-methoxy-1-methyl-ethylacetate.-   POL-03: ALNOVOL HPN100 a novolac resin obtained from CLARIANT GmbH.-   POL-04: DURITE PD443 is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-05: DURITE SD423A is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-06: DURITE SD126A is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-07: BAKELITE 6866LB02 is a novolac resin obtained from BAKELITE    AG.-   POL-08: BAKELITE 6866LB03 is a novolac resin obtained from BAKELITE    AG.-   POL-09: KR 400/8 is a novolac resin obtained from KOYO CHEMICALS    INC.-   POL-10: HRJ 1085 is a novolac resin obtained from SCHNECTADY    INTERNATIONAL INC.-   POL-11: HRJ 2606 is a phenol novolac resin obtained from SCHNECTADY    INTERNATIONAL INC.-   POL-12: LYNCUR CMM is a copolymer of 4-hydroxy-styrene and methyl    methacrylate obtained from SIBER HEGNER.

The polymer of the present invention may contain more than one: type ofa —S-(L)_(k)-Q group. In this situation each type of —S-(L)_(k)-Q groupscan be incorporated successively, or it is also possible to react amixture of different modifying reagentia. The preferred amount of eachtype of —S-(L)_(k)-Q group incorporated on the polymer is between 0.5mol % and 80 mol %, more preferably between 1 mol % and 50 mol %, mostpreferably 2 mol % and 30 mol %.

According to another aspect of the present invention, the above polymeris used in the coating of a lithographic printing plate precursor.According to one embodiment, the printing plate precursor ispositive-working, i.e. after exposure and development the exposed areasof the oleophilic layer are removed from the support and definehydrophilic, non-image (non-printing) areas, whereas the unexposed layeris not removed from the support and defines an oleophilic image(printing) area. According to another embodiment, the printing plateprecursor is negative-working, i.e. the image areas correspond to theexposed areas.

Other polymers, such as unmodified phenolic resins or phenolic resinswith another modification than described in the present invention, canalso be added to the coating composition. The polymer of the presentinvention is preferably added to the coating in a concentration range of5% by weight to 98% by weight of the total coating, more preferablybetween 10% by weight to 95% by weight.

If the heat-sensitive coating is composed of more than one layer, thepolymer of the present invention is present in at least one of theselayers, e.g. in a top-layer. The polymer can also be present in morethan one layer of the coating, e.g. in a top-layer and in anintermediate layer.

The support has a hydrophilic surface or is provided with a hydrophiliclayer. The support may be a sheet-like material such as a plate or itmay be a cylindrical element such as a sleeve which can be slid around aprint cylinder of a printing press. Preferably, the support is a metalsupport such as aluminum or stainless steel.

A particularly preferred lithographic support is an electrochemicallygrained and anodized aluminum support.

Graining and anodizing of aluminum lithographic supports is well known.The grained aluminum support used in the material of the presentinvention is preferably an electrochemically grained support. The acidused for graining can be e.g. nitric acid. The acid used for grainingpreferably comprises hydrogen chloride. Also mixtures of e.g. hydrogenchloride and acetic acid can be used.

The grained and anodized aluminum support may be post-treated to improvethe hydrophilic properties of its surface. For example, the aluminumsupport may be silicated by treating its surface with a sodium silicatesolution at elevated temperature, e.g. 95° C. Alternatively, a phosphatetreatment may be applied which involves treating the aluminum oxidesurface with a phosphate solution that may further contain an inorganicfluoride. Further, the aluminum oxide surface may be rinsed with anorganic acid and/or salt thereof, e.g. carboxylic acids,hydroxycarboxylic acids, sulfonic acids or phosphonic acids, or theirsalts, e.g. succinates, phosphates, phosphonates, sulfates, andsulfonates. A citric acid or citrate solution is preferred. Thistreatment may be carried out at room temperature or may be carried outat a slightly elevated temperature of about 30 to 50° C. A furtherpost-treatment involves rinsing the aluminum oxide surface with abicarbonate solution. Still further, the aluminum oxide surface may betreated with polyvinylphosphonic acid, polyvinylmethylphosphonic acid,phosphoric acid esters of polyvinyl alcohol, polyvinylsulfonic acid,polyvinylbenzenesulfonic acid, sulfuric acid esters of polyvinylalcohol, and acetals of polyvinyl alcohols formed by reaction with asulfonated aliphatic aldehyde. It is further evident that one or more ofthese post-treatments may be carried out alone or in combination. Moredetailed descriptions of these treatments are given in GB-A- 1 084 070,DE-A- 4 423 140, DE-A- 4 417 907, EP-A- 659 909, EP-A- 537 633, DE-A- 4001 466, EP-A- 292 801, EP-A- 291 760 and U.S. Pat No. 4,458,005.

According to another embodiment, the support can also be a flexiblesupport, which is provided with a hydrophilic layer, hereinafter called‘base layer’. The flexible support is e.g. paper, plastic film, thinaluminum or a laminate thereof. Preferred examples of plastic film arepolyethylene terephthalate film, polyethylene naphthalate film,cellulose acetate film, polystyrene film, polycarbonate film, etc. Theplastic film support may be opaque or transparent.

The base layer is preferably a cross-linked hydrophilic layer obtainedfrom a hydrophilic binder cross-linked with a hardening agent such asformaldehyde, glyoxal, polyisocyanate or a hydrolyzedtetra-alkylorthosilicate. The latter is particularly preferred. Thethickness of the hydrophilic base layer may vary in the range of 0.2 to25 μm and is preferably 1 to 10 μm.

The hydrophilic binder for use in the base layer is e.g. a hydrophilic(co)polymer such as homopolymers and copolymers of vinyl alcohol,acrylamide, methylol acrylamide, methylol methacrylamide, acrylic acid,methacrylic acid, hydroxyethyl acrylate, hydroxyethyl methacrylate ormaleic anhydride/vinylmethylether copolymers. The hydrophilicity of the(co)polymer or (co)polymer mixture used is preferably the same as orhigher than the hydrophilicity of polyvinyl acetate hydrolyzed to atleast an extent of 60% by weight, preferably 80% by weight.

The amount of hardening agent, in particular tetraalkyl orthosilicate,is preferably at least 0.2 parts per part by weight of hydrophilicbinder, more preferably between 0.5 and 5 parts by weight, mostpreferably between 1 parts and 3 parts by weight

The hydrophilic base layer may also contain substances that increase themechanical strength and the porosity of the layer. For this purposecolloidal silica may be used. The colloidal silica employed may be inthe form of any commercially available water dispersion of colloidalsilica for example having an average particle size up to 40 nm, e.g. 20nm. In addition inert particles of larger size than the colloidal silicamay be added e.g. silica prepared according to Stöber as described in J.Colloid and Interface Sci., Vol. 26, 1968, pages 62 to 69 or aluminaparticles or particles having an average diameter of at least 100 nmwhich are particles of titanium dioxide or other heavy metal oxides. Byincorporating these particles the surface of the hydrophilic base layeris given a uniform rough texture consisting of microscopic hills andvalleys, which serve as storage places for water in background areas.

Particular examples of suitable hydrophilic base layers for use inaccordance with the present invention are disclosed in EP-A- 601 240,GB—P- 1 419 512, FR—P- 2 300 354, U.S. Pat. No. 3,971,660, and U.S. Pat.No. 4,284,705.

It is particularly preferred to use a film support to which an adhesionimproving layer, also called support layer, has been provided.Particularly suitable adhesion improving layers for use in accordancewith the present invention comprise a hydrophilic binder and colloidalsilica as disclosed in EP-A- 619 524, EP-A- 620 502 and EP-A- 619 525.Preferably, the amount of silica in the adhesion improving layer isbetween 200 mg/m² and 750 mg/m². Further, the ratio of silica tohydrophilic binder is preferably more than 1 and the surface area of thecolloidal silica is preferably at least 300 m²/gram, more preferably atleast 500 m²/gram.

The coating provided on the support is heat-sensitive and can preferablybe handled in normal working lighting conditions (daylight, fluorescentlight) for several hours. The coating preferably does not containUV-sensitive compounds which have an absorption maximum in thewavelength range of 200 nm to 400 nm such as diazo compounds,photoacids, photoinitiators, quinone diazides, or sensitizers.Preferably the coating neither contains compounds which have anabsorption maximum in the blue and green visible light wavelength rangebetween 400 and 600 nm.

The coating may comprise one or more distinct layers. Besides the layersdiscussed hereafter, the coating may further comprise e.g. a “subbing”layer which improves the adhesion of the coating to the support, acovering layer which protects the coating against contamination ormechanical damage, and/or a light-to-heat conversion layer whichcomprises an infrared light absorbing compound.

A suitable negative-working alkaline developing printing plate comprisesa phenolic resin and a latent Bronsted acid which produces acid uponheating or IR radiation. These acids catalyze crosslinking of thecoating in a post-exposure heating step and thus hardening of theexposed regions. Accordingly, the non-exposed regions can be washed awayby a developer to reveal the hydrophilic substrate underneath. For amore detailed description of such a negative-working printing plateprecursor we refer to U.S. Pat. No. 6,255,042 and U.S. Pat. No.6,063,544 and to references cited in these documents. In such anegative-working lithographic printing plate precursor, the polymer ofthe present invention is added to the coating composition and replacesat least part of the phenolic resin.

In a positive-working lithographic printing plate precursor, the coatingis capable of heat-induced solubilization, i.e. the coating is resistantto the developer and ink-accepting in the non-exposed state and becomessoluble in the developer upon exposure to heat or infrared light to suchan extent that the hydrophilic surface of the support is revealedthereby.

Besides the polymer of the present invention, the coating may containadditional polymeric binders that are soluble in an aqueous alkalinedeveloper. Preferred polymers are phenolic resins, e.g. novolac,resoles, polyvinyl phenols and carboxy-substituted polymers. Typicalexamples of such polymers are described in DE-A-4007428, DE-A-4027301and DE-A-4445820.

In a preferred positive-working lithographic printing plate precursor,the coating also contains one or more dissolution inhibitors.Dissolution inhibitors are compounds which reduce the dissolution rateof the hydrophobic polymer in the aqueous alkaline developer at thenon-exposed areas of the coating and wherein this reduction of thedissolution rate is destroyed by the heat generated during the exposureso that the coating readily dissolves in the developer at exposed areas.The dissolution inhibitor exhibits a substantial latitude in dissolutionrate between the exposed and non-exposed areas. By preference, thedissolution inhibitor has a good dissolution rate latitude when theexposed coating areas have dissolved completely in the developer beforethe non-exposed areas are attacked by the developer to such an extentthat the ink-accepting capability of the coating is affected. Thedissolution inhibitor(s) can be added to the layer which comprises thehydrophobic polymer discussed above.

The dissolution rate of the non-exposed coating in the developer ispreferably reduced by interaction between the hydrophobic polymer andthe inhibitor, due to e.g. hydrogen bonding between these compounds.Suitable dissolution inhibitors are preferably organic compounds whichcomprise at least one aromatic group and a hydrogen bonding site, e.g. acarbonyl group, a sulfonyl group, or a nitrogen atom which may bequaternized and which may be part of a heterocyclic ring or which may bepart of an amino substituent of said organic compound. Suitabledissolution inhibitors of this type have been disclosed in e.g. EP-A825927 and 823327.

Water-repellent polymers represent an another type of suitabledissolution inhibitors. Such polymers seem to increase the developerresistance of the coating by repelling the aqueous developer from thecoating. The water-repellent polymers can be added to the layercomprising the hydrophobic polymer and/or can be present in a separatelayer provided on top of the layer with the hydrophobic polymer. In thelatter embodiment, the water-repellent polymer forms a barrier layerwhich shields the coating from the developer and the solubility of thebarrier layer in the developer or the penetrability of the barrier layerby the developer can be increased by exposure to heat or infrared light,as described in e.g. EP-A 864420, EP-A 950517 and WO99/21725. Preferredexamples of the water-repellent polymers are polymers comprisingsiloxane and/or perfluoroalkyl units. In one embodiment, the coatingcontains such a water-repellent polymer in an amount between 0.5 and 25mg/m², preferably between 0.5 and 15 mg/m² and most preferably between0.5 and 10 mg/m². When the water-repellent polymer is alsoink-repelling, e.g. in the case of polysiloxanes, higher amounts than 25mg/m² can result in poor ink-acceptance of the non-exposed areas. Anamount lower than 0.5 mg/m² on the other hand may lead to anunsatisfactory development resistance. The polysiloxane may be a linear,cyclic or complex cross-linked polymer or copolymer. The termpolysiloxane compound shall include any compound which contains morethan one siloxane group —Si(R,R′)—O—, wherein R and R′ are optionallysubstituted alkyl or aryl groups. Preferred siloxanes arephenylalkylsiloxanes and dialkylsiloxanes. The number of siloxane groupsin the (co)polymer is at least 2, preferably at least 10, morepreferably at least 20. It may be less than 100, preferably less than60. In another embodiment, the water-repellent polymer is ablock-copolymer or a graft-copolymer of a poly(alkylene oxide) block anda block of a polymer comprising siloxane and/or perfluoroalkyl units. Asuitable copolymer comprises about 15 to 25 siloxane units and 50 to 70alkylene oxide groups. Preferred examples include copolymers comprisingphenylmethylsiloxane and/or dimethylsiloxane as well as ethylene oxideand/or propylene oxide, such as Tego Glide 410, Tego Wet 265, TegoProtect 5001 or Silikophen P50/X, all commercially available from TegoChemie, Essen, Germany. Such a copolymer acts as a surfactant which uponcoating, due to its bifunctional structure, automatically positionsitself at the interface between the coating and air and thereby forms aseparate top layer even when the whole coating is applied from a singlecoating solution. Simultaneously, such surfactants act as a spreadingagent which improves the coating quality. Alternatively, thewater-repellent polymer can be applied in a second solution, coated ontop of the layer comprising the hydrophobic polymer. In that embodiment,it may be advantageous to use a solvent in the second coating solutionthat is not capable of dissolving the ingredients present in the firstlayer so that a highly concentrated water-repellent phase is obtained atthe top of the coating.

Preferably, also one or more development accelerators are included inthe coating, i.e. compounds which act as dissolution promoters becausethey are capable of increasing the dissolution rate of the non-exposedcoating in the developer. The simultaneous application of dissolutioninhibitors and accelerators allows a precise fine tuning of thedissolution behavior of the coating. Suitable dissolution acceleratorsare cyclic acid anhydrides, phenols or organic acids. Examples of thecyclic acid anhydride include phthalic anhydride, tetrahydrophthalicanhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride,maleic anhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride,succinic anhydride, and pyromellitic anhydride, as described in U.S.Pat. No. 4,115,128. Examples of the phenols include bisphenol A,p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone,2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone,4,4′,4″-trihydroxy-triphenylmethane, and 4,4′,3″,4″-tetrahydroxy-3,5,3′,5′-tetramethyltriphenyl-methane, and the like. Examples of the organicacids include sulfonic acids, sulfinic acids, alkylsulfuric acids,phosphonic acids, phosphates, and carboxylic acids, as described in, forexample, JP-A Nos. 60-88,942 and 2-96,755. Specific examples of theseorganic acids include p-toluenesulfonic acid, dodecylbenzenesulfonicacid, p-toluenesulfinic acid, ethylsulfuric acid, phenylphosphonic acid,phenylphosphinic acid, phenyl phosphate, diphenyl phosphate, benzoicacid, isophthalic acid, adipic acid, p-toluic acid, 3,4-dimethoxybenzoicacid, phthalic acid, terephthalic acid, 4-cyclohexene-1,2-dicarboxylicacid, erucic acid, lauric acid, n-undecanoic acid, and ascorbic acid.The amount of the cyclic acid anhydride, phenol, or organic acidcontained in the coating is preferably in the range of 0.05 to 20% byweight, relative to the coating as a whole.

The polymer of the present invention can be used in conventionalphotosensitive printing plate precursors wherein at least part of theconventional phenolic polymer is replaced by at least one of thepolymers of the present invention.

According to a more preferred embodiment, the material of the presentinvention is image-wise exposed to infrared light, which is convertedinto heat by an infrared light absorbing agent, which may be a dye orpigment having an absorption maximum in the infrared wavelength range.The concentration of the sensitizing dye or pigment in the coating istypically between 0.25 and 10.0 wt. %, more preferably between 0.5 and7.5 wt. % relative to the coating as a whole. Preferred IR-absorbingcompounds are dyes such as cyanine or merocyanine dyes or pigments suchas carbon black. A suitable compound is the following infrared dye:

The coating may further contain an organic dye which absorbs visiblelight so that a perceptible image is obtained upon image-wise exposureand subsequent development. Such a dye is often called contrast dye orindicator dye. Preferably, the dye has a blue color and an absorptionmaximum in the wavelength range between 600 nm and 750 nm. Although thedye absorbs visible light, it preferably does not sensitize the printingplate precursor, i.e. the coating does not become more soluble in thedeveloper upon exposure to visible light. Suitable examples of such acontrast dye are the quaternized triarylmethane dyes. Another suitablecompound is the following dye:

The infrared light absorbing compound and the contrast dye may bepresent in the layer comprising the hydrophobic polymer, and/or in thebarrier layer discussed above and/or in an optional other layer.According to a highly preferred embodiment, the infrared light absorbingcompound is concentrated in or near the barrier layer, e.g. in anintermediate layer between the layer comprising the hydrophobic polymerand the barrier layer.

The printing plate precursor of the present invention can be exposed toinfrared light with LEDs or a laser. Preferably, a laser emitting nearinfrared light having a wavelength in the range from about 750 to about1500 nm is used, such as a semiconductor laser diode, a Nd:YAG or aNd:YLF laser. The required laser power depends on the sensitivity of theimage-recording layer, the pixel dwell time of the laser beam, which isdetermined by the spot diameter (typical value of modern plate-settersat 1e² of maximum intensity : 10-25 μm), the scan speed and theresolution of the exposure apparatus (i.e. the number of addressablepixels per unit of linear distance, often expressed in dots per inch ordpi; typical value: 1000-4000 dpi).

Two types of laser-exposure apparatuses are commonly used: internal(ITD) and external drum (XTD) plate-setters. ITD plate-setters forthermal plates are typically characterized by a very high scan speed upto 1500 m/sec and may require a laser power of several Watts. The AgfaGalileo T is a typical example of a plate-setter using theITD-technology. XTD plate-setters operate at a lower scan speedtypically from 0.1 m/sec to 10 m/sec and have a typicallaser-output-power per beam from 20 mW up to 500 mW. The CreoTrendsetter plate-setter family and the Agfa Excalibur plate-setterfamily both make use of the XTD-technology.

The known plate-setters can be used as an off-press exposure apparatus,which offers the benefit of reduced press down-time. XTD plate-setterconfigurations can also be used for on-press exposure, offering thebenefit of immediate registration in a multi-color press. More technicaldetails of on-press exposure apparatuses are described in e.g. U.S. PatNos. 5,174,205 and 5,163,368.

In the development step, the non-image areas of the coating can beremoved by immersion in an aqueous alkaline developer, which may becombined with mechanical rubbing, e.g. by a rotating brush. Thedeveloper preferably has a pH above 10, more preferably above 12. Thedevelopment step may be followed by a rinsing step, a gumming step, adrying step and/or a post-baking step.

The printing plate thus obtained can be used for conventional, so-calledwet offset printing, in which ink and an aqueous dampening liquid issupplied to the plate. Another suitable printing method uses so-calledsingle-fluid ink without a dampening liquid. Single-fluid ink consistsof an ink phase, also called the hydrophobic or oleophilic phase, and apolar phase which replaces the aqueous dampening liquid that is used inconventional wet offset printing. Suitable examples of single-fluid inkshave been described in U.S. Pat. No. 4,045,232; U.S. Pat. Nos. 4,981,517and 6,140,392. In a most preferred embodiment, the single-fluid inkcomprises an ink phase and a polyol phase as described in WO 00/32705.

EXAMPLES

List of substitution reagentia used in the preparation of modifiedpolymers:

Sulfolane: tetrahydrothiophene 1,1-dioxide

Preparation of polymer MP-01:

Modifying solution:

To a mixture of 8.9 g MR-01 and 500 ml CH₂Cl₂, stirred at roomtemperature, 4.1 ml SO₂Cl₂ was added and the mixture was brought to 40°C. for 30 minutes after which the mixture was cooled to roomtemperature.

Phenolic polymer solution:

24.5 g of solid polymer, obtained by precipitation of 61.25 g of POL-01solution (40% by weight in Dowanol PM) in a mixture of water/methanol(volume ratio 10:1) and subsequent drying at 40° C., was added to amixture of 250 ml CH₂Cl₂ and 25 ml sulfolane at 40° C. After the polymerwas dissolved, the mixture was cooled to room temperature.

Then the above prepared modifying solution was added to the phenolicpolymer solution over a 45 minute period while continuously stirring.After addition the reaction mixture was stirred for another 60 minutesunder reflux conditions. Then the reaction mixture was cooled to roomtemperature and 750 ml acetone was added. Then, the reaction mixture wasconcentrated by evaporation until an oil was obtained. This oil was thenadded to 2 liters of ice-water over a 30 minute period whilecontinuously stirring. The polymer precipitated from the aqueous mediumand was isolated by filtration. The desired product was finally obtainedby washing with water and subsequent drying at 45° C.

Preparation of Polymer MP-02:

The preparation of polymer MP-02 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 14.8 g MR-02, 200 ml CH₂Cl₂ and 4.1 ml SO₂Cl₂ and inthe preparation of the phenolic polymer solution 24.5 g solid polymerand a mixture of 100 ml CH₂Cl₂ and 100 ml sulfolane were used instead ofthe products and the quantities given in the preparation of polymerMP-01.

Preparation of Polymer MP-05:

The preparation of polymer MP-05 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 10.5 g MR-05, 150 ml CH₂Cl₂ and 6.2 ml SO₂Cl₂ and inthe preparation of the phenolic polymer solution 36.8 g of solidpolymer, obtained by precipitation of 92 g of POL-01 solution, and amixture of 75 ml CH₂Cl₂ and 100 ml sulfolane were used instead of theproducts and the quantities given in the preparation of polymer MP-01.

Preparation of Polymer MP-06:

The preparation of polymer MP-06 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 12.5 g CMR-01, 150 ml CH₂Cl₂ and 6.2 ml SO₂Cl₂ and inthe preparation of the phenolic polymer solution 36.8 g solid polymerand a mixture of 100 ml CH₂Cl₂ and 100 ml sulfolane were used instead ofthe products and the quantities given in the preparation of polymerMP-01.

Preparation of Polymer MP-07:

The preparation of polymer MP-07 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 14 g CMR-02, 100 ml CH₂Cl₂ and 2.1 ml SO₂Cl₂ and inthe preparation of the phenolic polymer solution 24.5 g solid polymerand a mixture of 50 ml CH₂Cl₂, 100 ml sulfolane and 6.8 mltetramethylguanidine were used instead of the products and thequantities given in the preparation of polymer MP-01.

Preparation of Polymer MP-08:

The preparation of polymer MP-08 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 14.2 g CMR-03 and 100 ml CH₂Cl₂ and no addition ofSO₂Cl₂ and in the preparation of the phenolic polymer solution 36.8 gsolid polymer and a mixture of 100 ml CH₂Cl₂ and 50 ml sulfolane wereused instead of the products and the quantities given in the preparationof polymer MP-01.

Preparation of Polymer MP-09:

The preparation of polymer MP-09 was carried out in the same way as thatof polymer MP-01 with the exception that in the preparation of themodifying solution 7.95 g CMR-04, 150 ml CH₂Cl₂ and 6.2 ml SO₂Cl₂ and inthe preparation of the phenolic polymer solution 36.8 g solid polymerand a mixture of 75 ml CH₂Cl₂ and 75 ml sulfolane were used instead ofthe products and the quantities given in the preparation of polymerMP-01.

Test 1:

Preparation of the Coating:

A coating solution was prepared by mixing the following ingredients:

-   86.55 g Dowanol PM-   464.64 g methyl ethyl ketone-   101.28 g of a solution of the infrared dye IR-1 in a concentration    of 2% by weight in Dowanol PM-   144.70 g of a solution of the contrast dye CD-1 in a concentration    of 1% by weight in Dowanol PM-   159.14 g of a solution of Tego Glide 410 in a concentration of 1% by    weight in Dowanol PM-   159.14 g of a solution of a phenolic polymer, as listed in Table 1,    in a concentration of 40% by weight in Dowanol PM-   3.18 g of 3,4,5-trimethoxycinnamic acid.    The coating solution was coated on an electrochemically grained and    anodized aluminum substrate at a wet thickness of 20μm. The coating    was dried for 1 minute at 130° C.    For measuring the chemical resistance 2 different solutions were    selected:-   Test solution 1: solution of isopropanol in a concentration of 50%    by weight in water,-   Test solution 2: EMERALD PREMIUM MXEH, commercially available from    ANCHOR.    The chemical resistance was tested by contacting a droplet of 40 μl    of each test solution on different spots of the coating. After 3    minutes, the droplet was removed from the coating with a cotton pad.    The attack on the coating due to each test solution was rated by    visual inspection as follows:-   0: no attack,-   1: changed gloss of the coating's surface,-   2: small attack of the coating (thickness is decreased),-   3: heavy attack of the coating,-   4: completely dissolved coating.

The higher the rating, the less is the chemical resistance of thecoating. The results for the 2 test solutions on each coating aresummarised in Table 1. The table contains also information about thetype of the phenolic polymer used in the modifying reaction, the type ofmodifying reagens and the degree of modification (in mol %) and theMP-number of the prepared polymer. TABLE 1 Type TEST 1 TEST 1 Pheno-Degree Prep. Test Test Example lic Type modif. Polym. solu- solu- numberPolymer reagens (mol %) MP-nr. tion 1 tion 2 Comparative POL-01 — — — 44 example 1 Example 1 POL-01 MR-01 25 MP-01 0 1 Example 2 POL-01 MR-0225 MP-02 2 2 Example 5 POL-01 MR-05 25 MP-05 0 0 Comparative POL-01CMR-01 25 MP-06 4 3 example 2 Comparative POL-01 CMR-02 25 MP-07 4 3example 3 Comparative POL-01 CMR-03 25 MP-08 4 3 example 4 ComparativePOL-01 CMR-04 25 MP-09 4 3 example 5Table 1 demonstrates that the polymers, modified according to thepresent invention, give rise to a significant increase of the chemicalresistance of the coating compared with unmodified polymer and comparedwith polymers, modified for the same degree with a modifying reagenswhich does not contain a heterocyclic group.

1. a polymer comprising a phenolic monomeric unit wherein the phenylgroup of the phenolic monomeric unit is substituted by a group havingthe structure —S-(L)_(k)-Q wherein S is covalently bound to a carbonatom of the phenyl group, wherein L is a linking group, k is 0 or 1 andq comprises a heterocyclic group.
 2. A polymer according to claim 1wherein said heterocyclic group is aromatic.
 3. A polymer according toclaim 1 wherein said heterocyclic group contains at least one nitrogenatom in the ring of the heterocyclic group.
 4. A polymer according toclaim 1 wherein said heterocyclic group has a 5- or 6- membered ringstructure, and is optionally annelated with another ring system.
 5. Apolymer according to claim 1 wherein the heterocyclic group is selectedfrom an optionally substituted tetrazole, triazole, thiadiazole,oxadiazole, imidazole, benzimidazole, thiazole, benzthiazole, oxazole,benzoxazole, pyrazole, pyrrole, pyrimidine, pyrasine, pyridasine,triazine or pyridine group.
 6. A polymer according to claim 1 wherein—S-(L)_(k)-Q comprises the following formula

wherein Z represents the necessary atoms to form a 5- or 6- memberedheterocyclic aromatic group, and is optionally annelated with anotherring system.
 7. A polymer according to claim 6 wherein the —S-(L)_(k)-Qcomprises the following formula

wherein R¹ is selected from hydrogen or an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group.
 8. A polymer according to claim 6 wherein—S-(L)_(k)-Q comprises the following formula

wherein n is 0, 1, 2, 3, 4 or 5, wherein each R¹ is independentlyselected from hydrogen, an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen, —SO₂—NH—R,—NH—SO₂—R,—CO—NR—R,—NR—CO—R,—NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁵,—CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁵, —SO²—R², —SO—R⁵,—P(═O)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R²,—CN, —NO₂ or -M—R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, where in R² to R⁴ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁵ is an optionally substituted alkyl,alkenyl, alknyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴ and R⁵ together represent the necessary atoms to form acyclic structure.
 9. A polymer according to claim 6 wherein —S-(L)_(k)-Qcomprises the following formula

wherein X is 0, S or NR³, wherein R is selected from hydrogen, anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogenor -L¹—R², where in L¹ is a linking group, wherein R² is selected fromhydrogen, an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogenor —CN, wherein R³ is selected from hydrogen or an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, or wherein at least twogroups selected from R¹, R² and R³ represent the necessary atoms to forma cyclic structure.
 10. A polymer according to claim 6 wherein—S-(L)_(k)-Q comprises the following formula

wherein X is 0, S or NR⁴, wherein R¹and R² are independently selectedfrom hydrogen, an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, halogen or -L1—R3 wherein L¹ is a linking group, wherein R³ isselected from hydrogen, an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen or —CN, wherein R⁴ is selected fromhydrogen or an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, or wherein at least two groups selected from R¹, R², R³ and R⁴together represent the necessary atoms to form a cyclic structure.
 11. Apolymer according to claim 6 wherein the —S-(L)_(k)-Q comprises thefollowing formula

wherein n is 0, 1, 2, 3 or 4, wherein X is 0, S or NR⁵, wherein each R¹is independently selected from hydrogen, an optionally substitutedalkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R², —NH—SO₂—R⁶,—CO—NR²—R³, —NR²—CO—R⁶, —NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R³,—O—CO—NR²—R³, —O—CO—R⁶, —CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁶, —SO₂—R²,—SO—R⁶, —P(═o)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R²,—S—R², —CN, —NO₂ or -M—R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, wherein R² to R⁵ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁶ is an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴, R⁵ and R⁶ represent the necessary atoms to form a cyclicstructure.
 12. A polymer according to claim 6 wherein the —S-(L)_(k)-Qcomprises the following formula

wherein n is 0, 1, 2 or 3, wherein each R¹ is independently selectedfrom hydrogen, an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, halogen, —SO₂—NR—R², —NR—SO₂—R⁵, —CO—NR²—R³, —NR²—CO—R⁵,—NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁵,—CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁵, —SO₂—R², —SO—R⁵,—P(═O)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R²,—CN, —NO₂ or -M-R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, wherein R² to R⁴ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁵ is an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴ and R⁵ together represent the necessary atoms to form acyclic structure.
 13. A polymer according to claim 6 wherein the—S-(L)_(k)-Q comprises one of the following formula:


14. A polymer according to claim 1, wherein said polymer comprising aphenolic monomeric unit is a novolac, resol or polyvinylphenol.
 15. Aheat-sensitive lithographic printing plate precursor comprising asupport having a hydrophilic surface and an oleophilic coating providedon the hydrophilic surface, said coating comprising an infrared lightabsorbing agent and a polymer comprising a phenolic monomeric unitwherein the phenyl group of the phenolic monomeric unit is substitutedby a group having the structure —S-(L)_(k)-Q wherein S is covalentlybound to a carbon atom of the phenyl group, wherein L is a linking groupk is 0 or 1 and Q comprises a heterocyclic group.
 16. A heat-sensitivelithographic printing plate precursor according to claim 15, whereinsaid coating further comprises a dissolution inhibitor and wherein saidprecursor is a positive working lithographic printing plate precursor.17. A heat-sensitive lithographic printing plate precursor according toclaim 16, wherein said dissolution inhibitor is selected from the groupconsisting of an organic compound which comprises at least one aromaticgroup and a hydrogen bonding site, a polymer or surfactant comprisingsiloxane orperfluoroalkyl units and mixtures thereof.
 18. (canceled) 19.A heat-sensitive lithographic printing plate precursor according toclaim 15, wherein said coating further comprising a latent Brönsted acidand an acid-crosslinkable compound and wherein said precursor is anegative working lithographic printing plate precursor.
 20. (canceled)21. A polymer according to claim 2 wherein said heterocyclic groupcontains at least one nitrogen atom in the ring of the heterocyclicgroup.
 22. A polymer according to claim 2 wherein said heterocyclicgroup has a 5- or 6-membered ring structure, and is optionally annelatedwith another ring system.
 23. A polymer according to claim 3 whereinsaid heterocyclic group has a 5- or 6-membered ring structure, and isoptionally annelated with another ring system.
 24. A polymer accordingto claim 3 wherein said heterocyclic group has a 5- or 6-membered ringstructure, and is annelated with another ring system.
 25. A polymeraccording to claim 24 wherein the heterocyclic group is selected from anoptionally substituted tetrazole, triazole, thiadiazole, oxadiazole,imidazole, benzimidazole, thiazole, benzthiazole, oxazole, benzoxazole,pyrazole, pyrrole, pyrimidine, pyrasine, pyridasine, triazine orpyridine group.
 26. A polymer according to claim 5, wherein said polymercomprising a phenolic monomeric unit is a novolac, resol orpolyvinylphenol.
 27. A polymer according to claim 15 wherein theheterocyclic group is selected from an optionally substituted tetrazole,triazole, thiadiazole, oxadiazole, imidazole, benzimidazole, thiazole,benzthiazole, oxazole, benzoxazole, pyrazole, pyrrole, pyrimidine,pyrasine, pyridasine, triazine or pyridine group.
 28. A heat-sensitivelithographic printing plate precursor according to claim 15 wherein—S-(L)_(k)-Q comprises the following formula

wherein Z represents the necessary atoms to form a 5- or 6-memberedheterocyclic aromatic group, and is optionally annelated with anotherring system.
 29. A heat-sensitive lithographic printing plate precursoraccording to claim 28 wherein the —S-(L)_(k)-Q comprises the followingformula

wherein R¹ is selected from hydrogen or an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group.
 30. A heat-sensitive lithographic printing plateprecursor according to claim 28 wherein —S-(L)_(k)-Q comprises thefollowing formula

wherein n is 0, 1, 2, 3, 4 or 5, wherein each R¹ is independentlyselected from hydrogen, an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen, —SO₂—NH—R,—NH—SO₂—R,—CO—NR—R,—NR—CO—R,—NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R³, —O—CO—NR²—R³, —O—CO—R⁵,—CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁵, —SO²—R², —SO—R⁵,—P(═O)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R²,—CN, —NO₂ or -M—R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, where in R² to R⁴ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁵ is an optionally substituted alkyl,alkenyl, alknyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴ and R⁵ together represent the necessary atoms to form acyclic structure.
 31. A heat-sensitive lithographic printing plateprecursor according to claim 28 wherein —S-(L)_(k)-Q comprises thefollowing formula

wherein X is 0, S or NR³, wherein R is selected from hydrogen, anoptionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogenor -L¹-R², where in L¹ is a linking group, wherein R² is selected fromhydrogen, an optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl,heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkyl group, halogenor —CN, wherein R³ is selected from hydrogen or an optionallysubstituted alkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl,heteroaryl, aralkyl or heteroaralkyl group, or wherein at least twogroups selected from R¹, R² and R³ represent the necessary atoms to forma cyclic structure.
 32. A heat-sensitive lithographic printing plateprecursor according to claim 28 wherein —S-(L)_(k)-Q comprises thefollowing formula

wherein X is 0, S or NR⁴, wherein R¹ and R² are independently selectedfrom hydrogen, an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, halogen or -L1—R3 wherein L¹ is a linking group, wherein R³ isselected from hydrogen, an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, halogen or —CN, wherein R⁴ is selected fromhydrogen or an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, or wherein at least two groups selected from R¹, R², R³ and R⁴together represent the necessary atoms to form a cyclic structure.
 33. Aheat-sensitive lithographic printing plate precursor according to claim28 wherein —S-(L)_(k)-Q comprises the following formula

wherein n is 0, 1, 2, 3 or 4, wherein X is 0, S or NR⁵, wherein each R¹is independently selected from hydrogen, an optionally substitutedalkyl, alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl,aralkyl or heteroaralkyl group, halogen, —SO₂—NH—R², —NH—SO₂—R⁶,—CO—NR²—R³, —NR²—CO—R⁶, —NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R³,—O—CO—NR²—R³, —O—CO—R⁶, —CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁶, —SO₂—R²,—SO—R⁶, —P(═o)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R²,—S—R²—CN, —NO₂ or -M—R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, wherein R² to R⁵ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁶ is an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴, R⁵ and R⁶ represent the necessary atoms to form a cyclicstructure.
 34. A heat-sensitive lithographic printing plate precursoraccording to. claim 28 wherein —S-(L)_(k)-Q comprises the followingformula

wherein n is 0, 1, 2 or 3, wherein each R¹ is independently selectedfrom hydrogen, an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, halogen, —SO₂—NR—R², —NR—SO₂—R⁵, —CO—NR²—R³, —NR²—CO—R⁵,—NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R3, —O—CO—NR ²—R³, —O—CO—R⁵,—CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁵, —SO₂—R², —SO—R⁵,—P(═O)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²—R³, —O—R², —S—R²,—CN, —NO₂ or -M—R², wherein M represents a divalent linking groupcontaining 1 to 8 carbon atoms, wherein R² to R⁴ are independentlyselected from hydrogen or an optionally substituted alkyl, alkenyl,alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, wherein R⁵ is an optionally substituted alkyl,alkenyl, alkynyl, cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl orheteroaralkyl group, or wherein at least two groups selected from eachR¹, R², R³, R⁴ and R⁵ together represent the necessary atoms to form acyclic structure.
 35. A heat-sensitive lithographic printing plateprecursor according to claim 28 wherein —S-(L)_(k)-Q comprises thefollowing formula

wherein n is 0, 1, 2 or 3, wherein each R¹ is independently selectedfrom hydrogen, an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, halogen, —SO₂—NR—R², —NR—SO₂—R⁵, —CO—NR²—R³, —NR^(2—CO—R) ⁵,—NR²—CO—NR³—R⁴, —NR²—CS—NR³—R⁴, —NR²—CO—O—R3, —O—CO—NR²—R³, —O—CO—R⁵,—CO—O—R², —CO—R², —SO₃—R², —O—SO₂—R⁵, —SO₂—R², —SO—R⁵,—P(═O)(—O—R²)(—O—R³), —O—P(═O)(—O—R²)(—O—R³), —NR²R³, —O—R³, —S—R², —CN,—NO₂ or -M—R², wherein M represents a divalent linking group containing1 to 8 carbon atoms, wherein R² to R⁴ are independently selected fromhydrogen or an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, wherein R⁵ is an optionally substituted alkyl, alkenyl, alkynyl,cycloalkyl, heterocyclic, aryl, heteroaryl, aralkyl or heteroaralkylgroup, or wherein at least two groups selected from each R¹, R², R³, R⁴and R⁵ together represent the necessary atoms to form a cyclicstructure.
 36. A heat-sensitive lithographic printing plate precursoraccording to claim 16 wherein the heterocyclic group is selected from anoptionally substituted tetrazole, triazole, thiadiazole, oxadiazole,imidazole, benzimidazole, thiazole, benzthiazole, oxazole, benzoxazole,pyrazole, pyrrole, pyrimidine, pyrasine, pyridasine, triazine orpyridine group.
 37. A heat-sensitive lithographic printing plateprecursor according to claim 19 wherein the heterocyclic group isselected from an optionally substituted tetrazole, triazole,thiadiazole, oxadiazole, imidazole, benzimidazole, thiazole,benzthiazole, oxazole, benzoxazole, pyrazole, pyrrole, pyrimidine,pyrasine, pyridasine, triazine or pyridine group.